Previous studies indicate that heat increases the response of radioresistant tumors to ionizing radiation to a sufficient level such that they can be controlled. The objective of this research is to develop techniques combining thermal and ionizing radiation to provide greater enhancement of tumor cure. Tumor, normal tissues and cultured cells will be irradiated prior to exposures to variable temperatures. Fractionation studies of radiation alone and in combination with hyperthermia will be carried out to determine time-dose relationships of hyperthermia and ionizing radiation. Judicious combinations of temperature variations and irradiation may permit cures of tumors which appear to be relatively radioresistant and improved cure rates for tumors which are now considered radiocurable. Evaluations will be based on x radiation doses required to cure 50% of third generation transplants of a C3H mouse mammary adenocarcinoma. Evaluations of skin response of treated mice will be done. In vitro experiments will be done with synchronized and asynchronous Chinese hamster ovary cells. Some of these studies will also be carried out in vitro with cells derived from the mouse mammary tumor. During the course of the experiment, ultrasound techniques will be developed for localization of heat within tumor tissues.